Field of the Invention
The invention relates to a process of register adjustment or maintenance, with automatic initial register adjustment, of a web of preprinted material in processing machines.
By initial register adjustment is understood here the process during which, at each starting or restarting of the processing machine, the preprinted web and the processing tool are initially brought into register, i.e., under such a condition that the tool acts at each cycle at the desired point of the web, relative to the preprinted format that it carries. This register adjustment therefore implies, on the one hand, synchronization of the tool and web and, on the other hand, adjustment in position (generally angular, the tool being rotary) of the tool relative to the web.
In the art of printing and processing, or more generally of processing of a web of material, and to perform several operations on the same web of material, two types of machines are essentially known, namely, "on-line" machines and "off-line" machines.
On-line machines are machines, in which a blank web is processed at the beginning, and the web passes in successive work stations along a continuous path, in an essentially taut state, while the various tools are operated by the same shaft.
The "off-line" machines are machines in which a web that has already undergone a processing (generally a printing) is processed in a machine with one or more independent work stations.
The problems that on-line machines and off-line machines pose are fundamentally different.
The on-line machines are essentially stable by design, with the elements being in perfect synchronization with the printed pattern, because the printing groups are mechanically keyed on the same drive shaft as the processing tools. Performing all the operations at the same time on a blank web at the beginning avoids all the problems of register readjustment during restarting after a stop, accidental or not.
Once the machine has been adjusted so that the successive tools (starting from the 2nd, the first working on a blank web) will be in register with the web, the inevitable variations will occur in one direction and the other, around the position in correct register, even in the absence of any correction.
On the other hand, the off-line machines have an essentially unstable positioning. Essentially two problems arise for register adjustment of such a machine. First, it is necessary to make the speed of the web and the speed of the tools correspond to have one rotation of the tool for one advance of a paper printing (speed error) This problem has several origins, for example:
there is always slippage between the web and driving rollers,
the mechanical development of the machine is constant, while the length of repetition of the printing varies inside the same reel, and with greater variance during a large printing (group of reels).
Secondly, the processing tools must be brought into correct position relative to the printing (position error).
This problem is more significant in such an off-line machine. Actually, it is practically impossible, for example, to run or initially insert the preprinted web in register, which means that, after a break in the web for example, it is necessary to perform a new register adjustment.
Without an automatic correction system, the register of such a machine drifts as a function of the slippage, of the repetitive printing length and the like.
Once adjusted, the on-line machines essentially no longer have an adjustment problem, even after a stop or incident (paper break), all the stations in practice being "locked" relative to one another by the initial adjustment.
Such adjustment systems are known in the art, for example, from Adamson et al, U.S. Pat. No. 3,594,552 and Stratton et al, U.S. Pat. No. 4,318,176.
In a blank zone of the web there are placed register marks used to determine the position of the formats printed on the web relative to the working elements assuring the processing. These register marks have the form of printed marks, surrounded by blank printing zones, and photoelectric cells are placed in the machine, opposite the path of the marks, while an encoder is attached to the drive shaft of the working element.
The encoder supplies pulses whose relative position and frequency are linked to the position and speed of the working element, and these pulses are used to activate the signal of the photoelectric cell in a "window" extending over a predetermined distance on both sides of the ideal position or set point of the register mark relative to the working element.
The signal of the cell is analyzed in the window, in analog form, by a processor that identifies, relative to a background signal of the blank margin, the signal due to the register mark, a determination as to any deviation between the actual position and the set point position of the register mark is made, and then any correction to bring the register mark to the set point position is made.
This type of adjustment system assures a correct positioning of the register mark, and therefore a correct maintenance of the register adjustment, in the on-line machines, whose functioning is essentially stable, as is stated above, which causes the register mark, of course, to be kept within the limits of a rather narrow window on both sides of the register position.
The problem posed by off-line machines processing a preprinted web is basically different in that the functioning of such a machine is essentially unstable, as is stated above.
In known adjustment systems, of the abovementioned type, the processor which makes the adjustment may work in only a limited window, and therefore these types of systems do not allow automatic initial register adjustment, but, on the contrary, require a manual register adjustment, at least approximately so as to set the "window". Considering the unstable nature of off-line processing, the register mark constantly tends to leave this predefined window and, as soon as the register mark has left the window, the adjustment process must be stopped, to make a new approximate manual register adjustment of the window. This is the case after a break of the web as well. This obviously is costly in time and materials (spoilage of the preprinted web).
Therefore there is a need for a process and apparatus for assuring an automatic register adjustment, or an initial register adjustment, in an off-line machine working on a preprinted web, and assuring maintenance of the register adjustment under the unstable operating conditions of these machines.
To solve this problem and to make possible an automatic initial register adjustment, it is not sufficient to extend for a complete cycle the extent of the window in which the cell signal is analyzed. Actually, according to the prior art, analysis of the cell signal or other detector is limited to a window which is selected so that the register mark with the selected format appears there alone, in a quite distinct and isolated manner (for example, from other register marks of colors or the like also being able to be required for later printing and processing).
To solve this problem it is necessary therefore, besides extending the window for a complete cycle, to find a process and apparatus which makes it possible to identify reliably the format register mark relative to the background signal.
We also note that existing registers function only from a determined speed threshold (i.e., .+-.20% of maximum speed).
To minimize spoilage, it is advantageous to proceed to the register adjustment or readjustment at slow speed (i.e., .+-.3% of maximum speed), then to rise, in register, to the production speed.
Manual adjustment causes considerable spoilage. Further, it has the drawback of depending on the skill of the operator and, when the machine comprises a single shaft and several successive work stations, it is complicated by the fact that the upstream adjustment has an impact, of course, on the downstream stations, with the necessity of making this adjustment successively from upstream to downstream, which increases the spoilage and risks of error. Additionally, this operation must be repeated after each production accident such as a break in the web.
According to the invention, it is proposed to provide a process and apparatus of adjustment, with automatic initial register adjustment, of a preprinted web relative to a working element, operating independently of the machine speed, from the slow start of the machine to the maximum speed, and assuring the register adjustment after several operating cycles, to reduce the inevitable spoilage.
Besides simplifying the register adjustment and reducing spoilage, the process and apparatus of the invention makes it possible to identify one register mark among others, and easily to go from one register mark to another register mark, for example, of a different width, or again to define the register mark by a part of the printed format itself, so as to be able to eliminate the margin of the web which normally should remain free of printing, with the exception of the register marks, and thus reduce rejects of material.
It is important to stress here the difference between existing registers, which position a window relative to a register mark which are freely "chosen" from others, printed on a blank margin of the web, and the process of the invention, which identifies among others a register mark that is imposed by the operator, and that is not necessarily on a blank margin, but can be all or part of the preprinted format itself.
Actually, the known systems do not identify a specific register mark, but merely make the window move until there falls within it a printed mark giving a signal satisfactory for acting as a register mark (generally, a printed mark with a minimum blank zone on both sides). Generally, there will be several marks that are thus satisfactory over the length of the format and, in case of a considerable deviation, for example, the system can thus go from its register mark to another mark, giving an equivalent signal but causing a loss of register adjustment.
A purpose of the invention therefore is to provide a process of register adjustment or maintenance of a continuous web of material in a processing station of a machine, by means of register marks provided on the web, and an index pulse of the processing element of said station, in which a position pulse train is produced whose position relative to the index pulse is an instantaneous position measurement of the processing element during each of its cycles, and whose frequency is a measurement of its speed of movement, a detector signal is picked up, which is a function of a difference in characteristic between the background of the web and the marks that it carries, from which the deviation between the actual position and the set point position of the register mark is determined and, from the deviation thus determined, the desired correction to bring the deviation back to zero is applied. This process comprising, to allow automatic initial register adjustment and maintenance of a preprinted web, the steps of:
selecting a register mark over the length of the printed format, and determining its set point position,
determining and storing, in the form of a numerical sequence, at least one characteristic of the register mark selected, acting on a detected signal,
continuously sampling the detector signal synchronously with the position pulses, between the index pulses, and writing the results in memory, in the form of numerical values, at successive addresses,
periodically analyzing the memory contents to locate in it the sequence of numerical values corresponding best to that determined as a function of the register mark selected, and
calculating the deviation between the actual position and the set point position of the register mark from a determined address of said sequence and from the position of the processing element associated with it.
According to another feature of the process and apparatus of this invention, the characteristics of the register mark selected are its width, in the direction of travel of the preprinted web, and its shape, and there is calculated from its width the number of position pulses, and therefore of memory addresses, on which it extends, and a sequence of theoretical numerical values for the sampled detector signal are determined from its shape.
According to another embodiment of the process and apparatus of the invention, the characteristics of the selected register mark are its width, in the direction of travel of the preprinted web, and its color, and there is calculated from its width a number of position pulses, and therefore of memory addresses, on which it extends, and a sequence of theoretical numerical values for the sampled detector signal are determined from its color.
According to another embodiment, each index pulse causes the writing in memory of the subsequent numerical values to , successive addresses, whose origin is the start address of the memory.
According to another embodiment, analysis of the memory contents consists in calculating, in a first register adjustment mode, or initial register adjustment, at each address of the memory and over the extent of a complete cycle of the machine, from the central address of the sequence considered, a function of the sequence of the theoretical numerical values and of the sequence of actual numerical values, exhibiting a minimum or a maximum when the detected register mark exhibits the same width and the same shape or color as the predefined register mark, and in retaining the minimum of the minima or the maximum of the maxima associated with the corresponding address, the latter representing said desired central address.
According to another embodiment, since the operations of reading and writing in memory are exclusive, and analysis of the memory contents therefore interrupts the writing operation, analysis of the memory contents for a given cycle (i) begins after writing in memory, during this cycle, of the numerical value to which address (Xk) of the memory has been assigned which is the last of those corresponding to the analysis period, and therefore of nonwriting, of the preceding cycle (i-1), and the analysis is directed toward numerical values covering one cycle of the machine, and going from the following address (Xk+1) to said address (Xk), by considering the memory as a closed loop.
According to another embodiment, there is defined an adjustment zone extending over an interval exhibiting a predefined maximum deviation on both sides of the theoretical position of the register mark relative to the processing element and, when the correction has brought the register mark into this zone, the memory contents are analyzed, in a second adjustment mode, over a corresponding reduced zone.
According to yet another embodiment, the deviation between the closest value and the theoretical value is compared, and when this deviation is greater than a predefined value, the adjustment mode is deactivated to analyze the entire memory contents, according to the process of the register adjustment mode.